Although the Internet has had great successes in facilitating communications between computer systems and enabling electronic commerce, the computer systems connected to the Internet have been under almost constant attack by hackers seeking to disrupt their operation. Many of the attacks seek to exploit vulnerabilities of software systems including application programs or other computer programs executing on those computer systems. Developers of software systems and administrators of computer systems of an enterprise go to great effort and expense to identify and remove vulnerabilities. Because of the complexity of software systems, however, it is virtually impossible to identify and remove all vulnerabilities before software systems are released. After a software system is released, developers can become aware of vulnerabilities in various ways. A party with no malicious intent may identify a vulnerability and may secretly notify the developer so the vulnerability can be removed before a hacker identifies and exploits it. If a hacker identifies a vulnerability first, the developer may not learn of the vulnerability until it is exploited—sometimes with disastrous consequences.
Regardless of how a developer finds out about a vulnerability, the developer typically develops and distributes to system administrators “patches” or updates to the software system that remove the vulnerability. If the vulnerability has not yet been exploited (e.g., might not be known to hackers), then a developer can design, implement, test, and distribute a patch in a disciplined way. If the vulnerability has already been widely exposed, then the developer may rush to distribute a patch without the same care that is used under normal circumstances. When patches are distributed to the administrators of the computer systems, they are responsible for scheduling and installing the patches to remove the vulnerabilities.
Unfortunately, administrators often delay the installation of patches to remove vulnerabilities for various reasons. When a patch is installed, the software system and possibly the computer system on which it is executing may need to be shut down and restarted. If the vulnerability is in a software system that is critical to the success of an enterprise, then the administrator needs to analyze the tradeoffs of keeping the software system up and running with its associated risk of being attacked and of shutting down a critical resource of the enterprise to install the patch. Some administrators may delay the installation of the patch because they fear that, because of a hasty distribution, it might not be properly tested and have unintended side effects. If the patch has an unintended side effect, then the software system, the computer system, or some other software component that is impacted by the patch may be shut down by the patch itself. Administrators need to factor in the possibility of an unintended side effect when deciding whether to install a patch. These administrators may delay installing a patch until experience by others indicates that there are no serious unintended side effects.
Intrusion detection systems have been developed that can be used to identify whether an attempt is being made to exploit a known vulnerability that has not yet been patched. These intrusion detection systems can be used to prevent exploitations of newly discovered vulnerabilities for which patches have not yet been developed or installed. These intrusion detection systems may define a “signature” for each way a vulnerability can be exploited. For example, if a vulnerability can be exploited by sending a certain type of message with a certain attribute, then the signature for that exploitation would specify that type and attribute. When a security enforcement event occurs, such as the receipt of a message, the intrusion detection system checks its signatures to determine whether any match the security enforcement event. If so, the intrusion detection and/or prevention system may take action to prevent the exploitation, such as dropping the message.
The collection of signatures for an enterprise forms the security policy of that enterprise. A security policy is typically expressed as rules that each have a condition indicating when the rule is satisfied and one or more actions to be performed when the rule is satisfied. The condition of a rule may include signatures or other detection criteria.
Security policies are typically distributed by the developers of the security policies to the administrators of enterprises for implementation on the computer systems of the enterprises. The administrators may have the flexibility to customize the security policies according to the needs of the enterprises. For example, a rule of a security policy may indicate to block a user's access to sports-related web sites. If, however, the enterprise is engaged in a sports-related industry, the administrator may want to disable that rule. After customizing the security policy, the administrator distributes the custom security policy to the computer systems of the enterprise. An administrator may be allowed to customize a security policy by modifying parameters of a detection criterion (e.g., remove a web site that should not be classified as sports-related) or the actions of a rule. In addition, an administrator may be allowed to add new rules. The security policy that is distributed to computer systems of an enterprise is the security policy of the developer as customized by the administrator.
Several difficulties are encountered when customizing and distributing security policies. First, when the developer releases an updated version of a security policy, the administrator would need to again modify the updated version to implement the customizations. Modifying security policies can be a time-consuming and error-prone process. Second, the delay between release of the updated version and distribution to computer systems of the enterprise resulting from modification of the security policy means that the computer systems may be subject to exploitation of vulnerabilities during the delay that the updated version is designed to prevent. It would be desirable to have a technique for customizing and distributing security policies that overcome one or more of these or other difficulties.